Conventionally, epoxy resins are used widely in the electronic material fields as an epoxy resin composition in combination with a curing agent. Among the electronic material fields, for example, in the applications such as a high refractive-index layer in an antireflective film (an antireflective film for a liquid crystal display and the like), an optical thin film (such as a reflecting plate), a sealant for electronic parts, a printed wiring substrate, and an interlayer insulation film material (an interlayer insulation film material for a built-up printed substrate, and the like), performances such as high adhesion to a base material, hard coating property, high heat resistance, and high transparency for visible light are required for a molding material.
Epoxy resin compositions containing an epoxy resin with a photoacid generator and a thermal acid generator use no solvent, and can cure the epoxy resin alone, so that in recent years, many studies have been performed over the epoxy resin compositions. Particularly, cationic photocuring with an ultraviolet ray is extremely excellent in terms of requiring no large oven for curing and injecting a small amount of energy.
Although alicyclic epoxy compounds having an epoxy group only in the alicyclic structure has high reactivity for cationic curing using light, so that such an alicyclic epoxy compound is widely used for cationic curing, the structure thereof is rigid, so that a cured product thereof tends to become rigid and brittle.
Glycidyl ether-type or glycidyl ester-type epoxy compounds that are conventional general-purpose epoxy compounds, represented by bisphenol-type epoxy compounds, have low reactivity relative to an acid generator and consequently, the reaction therebetween takes much time, so that such epoxy compounds have been generally considered as not suitable for cationic curing.
A resin containing a carboxy group produced using an epoxy alkyl ester of a cyclohexane dicarboxylic acid having an epoxy group as a crosslinkable compound has been disclosed (see Patent Document 1).